This invention relates to a transversal engine four-wheel drive vehicle.
Generally, there is created rotational speed difference accompanied by difference in a turning radius between front wheels and rear wheels in turning of a vehicle. In a part-time type four-wheel drive vehicle having no center differential (an operating device for dividing a power to a front wheel drive shaft and a rear wheel drive shaft), when the vehicle is turned under a four-wheel drive condition on a paved road where slippage between a road surface and drive wheels is hardly created, there is disadvantageously generated a return torque (rotational difference of the drive shafts) between the front wheel drive shaft and the rear wheel drive shaft. For this reason, in case of running on a road of high coefficient of friction such as a paved road, four-wheel drive is switched to two-wheel drive for purposes of preventing tight-corner braking due to the return torque in turning of the vehicle.
In the conventional part-time type four-wheel drive vehicle having a transversal engine, selection between the two-wheel drive and the four-wheel drive is carried out by engaging and releasing an engagement type clutch such as a dog clutch between one side power transmission member for normally transmitting a power to either side of front wheels or rear wheels, or a power transmission member to be driven in receipt of the power from the one side power transmission member and the other side power transmission member for transmitting the power to the other side.
Therefore, the conventional part-time type four-wheel drive vehicle has the following problems in view of selection between the two-wheel drive and the four-wheel drive.
(1) In case of a manual transmission, as the selection between the two-wheel drive and the four-wheel drive during running of the vehicle must be carried out under disengagement of a clutch, it is impossible to effect the selection under a slip condition of wheels.
(2) In case of an automatic transmission such as a planetary gear transmission and a V-belt type CVT, the selection between the two-wheel drive and the four-wheel drive during running of the vehicle must be carried out after setting a transmission range to a neutral condition. Therefore, the selection must be usually carried out during stop of the vehicle.
(3) As operational action of the engagement type clutch is large, it is difficult to carry out electrical or hydraulic operating control without manual operation.